1. Field of the Invention
This invention relates to a liquid jet recording head which ejects liquid to produce flying liquid droplets to record.
2. Description of the Prior Art
Ink jet recording techniques (liquid jet recording methods) have recently attracted attention since they generate negligible noise upon recording, enable high speed recording and can record on plain paper without any special fixation treatment.
Among such techniques, for example, the liquid jet recording method disclosed in Japanese Patent Laid-open No. 51837/1979 and German Patent Laid-open (DOLS)No. 2843064 is different from other liquid jet recording method in that heat energy is applied to liquid to produce a driving force for ejecting liquid droplets.
That is, the above-mentioned recording method comprises applying heat energy to a liquid to cause an abrupt increase in the volume of the liquid, ejecting the liquid from the orifice at the front of the recording head to form flying liquid droplets and attaching the droplets to a record receiving member to effect recording.
In particular, the liquid jet recording method disclosed in DOLS 2843064 can be not only effectively suitable for so-called "drop-on-demand" recording methods, but also enables to realization of a high density multi-orifice recording head of a full-line type, and therefore, images of high resolution and high quality can be produced at a high speed.
The recording head portion of an apparatus used for the above-mentioned recording method comprises a liquid ejecting portion constituted of an orifice for ejecting liquid and a liquid flow path containing, as a part of the construction, a heat actuating portion communicated with the orifice and applying heat energy to the liquid for ejecting liquid droplets, and an electrothermal transducer for generating heat energy.
The electrothermal transducer is provided with a pair of electrodes and a resistive heater layer connected to the electrodes and having a region generating heat (heat generating portion) between the electrodes.
A typical embodiment of the structure of such a liquid jet recording head is shown in FIGS. 1A, 1B, 1C and 1D.
FIG. 1A is a partial front view of the liquid jet recording head viewed from the orifice side, and FIGS. 1B, 1C and 1D are partial cross sectional views of different configurations taken along the dot and dash line XY of FIG. 1A.
Recording head 100 is constituted of orifice 104 and liquid ejecting portion 105 formed by bonding the surface of substrate 102 provided with electrothermal transducer 101 to a grooved plate 103 having a predetermined number of grooves having a predetermined width and depth at a predetermined line density such that the grooved plate covers the substrate. In FIG. 1, the recording head has a plurality of orifices 104, but the present invention is not limited to such an embodiment and a recording head having a single orifice is also within the scope of the present invention.
Liquid ejecting portion 105 has orifice 104 ejecting liquid at the end and heat actuating portion 106 where thermal energy generated by electrothermal transducer 101 is applied to liquid to form a bubble and where an abrupt state change due to expansion and shrinkage of the volume occurs.
Heat actuating portion 106 is located above heat generating portion 107 of electrothermal transducer 101, and a heat actuating surface 108 where heat generating portion 107 contacts the liquid is the bottom surface of the heat actuating portion 106.
Heat generating portion 107 is constituted of lower layer 109 provided on support 115, resistive heater layer 110 provided on lower layer 109, and first protective layer 111 provided on resistive heater layer 110. Resistive heater layer 110 is provided with electrodes 113 and 114 for flowing electric current to the layer 110 to generate heat. Electrode 113 is an electrode common to heat generating portions of liquid ejecting portions, and electrode 114 is a selection electrode for selecting the heat generating portion of each liquid ejecting portion to generate heat and is provided along the liquid flow path of each liquid ejecting portion.
First protective layer 111 serves to chemically and physically protect resistive heater layer 110 from the liquid at the heat generating portion 107 by isolating resistive heater layer 110 from the liquid in the liquid flow path at liquid ejecting portion 105, and also prevents short-circuits between electrodes 113 and 114 through the liquid. Thus, first protective layer 111 serves to protect resistive heater layer 110. First protective layer 111 also serves to prevent electric leakage between adjacent electrodes. In particular, it is important to prevent electric leakage between selection electrodes and electrolytic corrosion of electrodes caused by electric current flowing in an electrode resulting from contact of an electrode under the liquid flow path with the liquid, which may happen. Therefore, such a first protective layer 111 having a protective function is provided on at least an electrode which is disposed under a liquid flow path.
The upper layer including the first protective layer is required to have various properties depending on the position to be disposed. That is, for example the following characteristics are required at heat generating portion 107:
1) heat resistance, PA1 2) liquid resistance, PA1 3) liquid penetration prevention, PA1 4) thermal conductivity, PA1 5) oxidation prevention, PA1 6) insulation, and PA1 7) breakage prevention.
At portions other than heat generating portion 107, sufficiently high liquid penetration preventing property, liquid resistance and breakage preventing property are required, while resistance to stringent thermal conditions is not required.
However, at present there is not any material for constituting the upper layer capable of sufficiently satisfying all the characteristics 1)-7) as mentioned above. It is the present status that some of the conditions 1)-7) are not severely requested. For example, at heat generating portion 107, materials are selected by giving priority to conditions 1), 4) and 5) while, at portions other than heat generating portion 107, for example, at electrode portions, materials are selected by giving priority to conditions 2), 3) and 7), and the materials thus selected are disposed on the corresponding region surfaces to form the upper layer.
Apart from the above, in the case of a liquid jet recording head of a multi-orifice type, since a number of fine electrothermal transducers are formed on the substrate simultaneously, formation of each layer of the substrate and removal of a part of the formed layer are repeated, and as a result, the surface on which each layer in the upper layer is to be formed becomes a fine uneven surface having step edge portions, and therefore, the step coverage property of the layers in the upper layer at the step edge portions becomes important. In other words, when the step coverage property at the step edge portions is poor, penetration of the liquid occurs at the portions and causes electrolytic corrosion or dielectric breakdown. Further, the formed upper layer can suffer from the formation of defects upon fabrication with a considerable probability, and penetration of liquid through the defective portions results in shortening the life of the electrothermal transducer to a great extent.
In view of the foregoing, it is required that the upper layer has a good step coverage property at the step edge, defects such as pinholes and the like occur in the formed layer with only a low probability and even if the detects are formed, the number of defects is negligible.
In order to satisfy those requisites, heretofore the upper layer has been produced by laminating the first protective layer composed of an inorganic insulating material and the third protective layer composed of an organic material, or the first protective layer is constituted of two layers, that is, an under layer composed of an inorganic insulting material and an above layer composed of an inorganic material of high toughness, relatively excellent mechanical strength and having adhesion and cohesion to the first protective layer and the third protective layer, such as metals and the like, or the second protective layer composed of an inorganic material such as metals and the like overlies the third protective layer.
Though the third protective layer composed of an organic material is excellent in coating property, the heat resistance is poor so that the third protective layer can not be provided on the resistive heater layer at the heat generating portion. On the contrary, the second protective layer composed of an inorganic material such as metals is provided over the whole surface as an outermost surface layer of the substrate, or only on the resistive heater layer of the heat generating portion. When the second protective layer is provided in such a manner as the latter, but the third protective layer 112 does not overlap the second protective layer 116 as shown in FIG. 1B, there is only the first protective layer at portion b and therefore, sufficient protection can not be provided. Further, potential is locally concentrated to that portion and eventually, the electrode layer begins to dissolve; that is, corrosion resistance deteriorates. Even if the third protective layer overlaps the second protective layer, as far as the overlapping width is small as illustrated in FIGS. 1C and 1D, the liquid penetrates and potential is concentrated when the liquid soaking time is long, and therefore, dissolution of the electrode portion occurs. On the contrary, when the overlapping width is too large, the following problems occur. As shown in FIG. 1E, when, in the vicinity of the heat generating portion, second protective layer 116 composed of an inorganic material such as metals and the like is provided below third protective layer 112 composed of an organic material and on the first protective layer 111, the probability of occurrence of short between second protective layer 116 and electrode 113 or 114 disadvantageously increases and the yield of the products is extremely decreased. As shown in FIG. 1F, when opposite to FIG. 1E, the upper layer in the vicinity of the heat generating portion are laminated such that third protective layer 112 overlies first protective layer 111 and second protective layer 116 overlies the third protective layer, the liquid penetrates from the liquid flow path and exfoliation of the organic material layer (the protective layer) proceeds due to the stress of the inorganic material layer (the second protective layer).
On the other hand, the liquid is vaporized by heating at heat actuating portion 106, but the vapor is immediately cooled to condense since it is a subcooled boiling and the heating time is short. Therefore, bubble formation and condensation are repeated at a high frequency of several thousand times per sec. in the vicinity of the heat actuating surface, and the pressure change caused here can break the substrate (cavitation corrosion).
Since printed letters or signs of high image quality high density have been recently demanded, and there are required more precise processing of minute portions such as electrodes, resistive heater layers, accompanying protective layers and the like.